The present invention generally relates to image and video processing. More specifically, the present invention relates to one or more methods for edge-adaptive and recursive non-linear filtering of ringing effect and “mosquito noise” artifacts on images and video. Furthermore, the present invention also relates to one or more computerized systems that can operate and execute a method for edge-adaptive and recursive non-linear filtering of ringing effect and “mosquito noise” artifacts on various types of images and videos, regardless of which multimedia standards are utilized for encoding, decoding, compression, and/or decompression of various types of images and videos.
In image and video signal processing, a “ringing effect” is an undesirable and inaccurate visual clutter that tends to appear in contrasting pixel transition levels in an image. Sometimes also called “Gibbs effect,” or “mosquito noise” if the ringing effect is multi-dimensional, the ringing effect is generally caused by sharply filtering a wide-bandwidth signal. An image in a compressed format, for example, is subject to heavy quantization after a discrete cosine transform (DCT), and tends to exhibit the ringing effect. Furthermore, today's compression schemes for video signals inherently utilize low-pass filters in horizontal, vertical, and/or temporal domains. Unfortunately, the utilization of conventional linear low-pass filters also tends to distort the visual impact of an image transition, such as a transition from a darker area to a brighter area of an image sequence in a video file.
With popularity of JPEG (Joint Photographic Expert Group) and MPEG (Moving Picture Experts Group) formats in the last twenty years in digitized imaging and videos for computers, televisions, and other electronic devices, a number of conventional de-ringing filters have been devised to reduce the ringing effects in images and videos. The conventional de-ringing filters generally utilize linear low-pass filters and micro blocks to reduce the ringing effects. However, these conventional de-ringing filters have several disadvantages and inconveniences.
For example, a conventional de-ringing filter is typically designed in a loop with other image or video processing steps, and cannot easily be separated from the rest of the image or video processing steps. In many cases, separation of the conventional de-ringing filter from other image or video processing steps is not feasible. Therefore, conventional methods of reducing single or multi-dimensional ringing effects often involve an image or video compression standard-specific de-ringing filter. Utilizing a conventional image or video compression standard-specific de-ringing filter may be often inconvenient, cumbersome, or impractical in today' image and/or video processing systems that are supposed to handle a wide variety of image and video compression standards. Furthermore, in many instances, multi-dimensional ringing effects (e.g. dotted haze as “mosquito noise” in horizontal and vertical domains, flickers in some video data involving horizontal, vertical, and time domains, and etc.) are difficult to reduce using a conventional linear de-ringing filter, because finding a block edge after decoding a compressed image or video is often difficult.
In addition, in case of MPEG files, the motion compensation in MPEG video processing makes the multi-dimensional ringing effects (e.g. dotted haze in a frame, flickers in a plurality of frames in video data, other mosquito noise, and etc.) less evident in the original blocks, which in turn causes block-based conventional de-ringing filters less effective in removing the ringing effects. Moreover, conventional linear low-pass filters used as de-ringing filters typically reduce the resolution of the original image content while filtering out the ringing effects, because the conventional linear low-pass filters typically lower the quality of high-frequency content transitions. Furthermore, conventional linear low-pass filters are also unable to reduce high frequencies without introducing echoes or multiple repetitions of the original transition in decreasing levels for a decoded image or video content due to Gibbs effect.
Although certain conventional filters, such as various types of Gaussian filters, do not exhibit ringing effect, their frequency response is generally considered too progressive for effective application without substantial corrective algorithms in a video processing system. Furthermore, when low-pass filtering is required in more than one dimension—in the horizontal and vertical domains, for example—the ringing artifacts due to the two low-pass filters can create interference artifacts that appear as minima and maxima of brightness. These interference artifacts appear as the “mosquito noise” in a video footage. The mosquito noise is particularly pronounced in marginally-performing video compression and decompression devices that exhibit multiple performance compromises, which often act like a series of low-pass filters in multiple dimensions due to a need for a minimal bit-rate of each compressed image.
Some video compression standards, such as MPEG2 which is used for most digital broadcast television, do not include any provisions to reduce mosquito noise. More recent compression standards, such as HEVC, do include provisions to reduce these artifacts, mostly by an in-loop process in the encoder. However, because the older MPEG2 standard and other video and imaging compression standards are still widely used, providing a novel de-ringing filter that can reduce or filter out ringing effects for a wide variety of image and/or video compression standards may be highly desirable.
Furthermore, because there is also a growing demand for higher bandwidth in video processing, it may be also desirable to provide a non-linear, edge-adaptive, and compression standard-independent de-ringing filter that can effectively reduce undesirable ringing artifacts for a variety of video and imaging compression standards. Moreover, it may also be desirable to provide the non-linear, edge-adaptive, and compression standard-independent de-ringing filter as a process that can be executed on various forms of electronic hardware and software. In addition, it may be also be desirable to provide a related computer-implemented method for a non-linear and edge-adaptive recursive filtering of ringing effects in image and video processing.